In the fabrication of electronic devices, a film etching is performed in order to process a film of a workpiece or to remove unnecessary film. For example, etching a silicon oxide film is performed. As a method of etching the silicon oxide film, a chemical oxide removal (COR) process has been used.
In the COR process, a workpiece having a silicon oxide film is disposed inside a first chamber. Then, an HF gas and an NH3 gas are supplied into the first chamber. The HF gas and the NH3 gas thus supplied react with the silicon oxide film to form a reaction product. Subsequently, the workpiece having the reaction product formed thereon is heated inside a second chamber. As the workpiece is heated, the reaction product is sublimated and exhausted. As a result, the silicon oxide film is etched
In general, a flow rate of a gas supplied into a chamber is controlled to become a set flow rate by a flow rate controller. As in the above-described COR process, even in etching for subliming and removing a reaction product produced from a film by using two or more kinds of gases, the flow rate of the gas supplied into the chamber is controlled to become a set flow rate by the flow rate controller. In such etching, the accuracy of the flow rate control performed by the flow rate controller involves the result of etching of a film of a workpiece. Therefore, the flow rate controller is calibrated such that the gas is supplied into the chamber at the set flow rate.
As a method of calibrating the flow rate controller, a build-up method is known. In such a build-up method, an increase rate of an internal pressure of a chamber is obtained in a state in which a gas, whose flow rate is adjusted by a flow rate controller, is supplied into the chamber. Based on the obtained increase rate, a current flow rate of the gas supplied into the chamber is measured. The flow rate controller is calibrated using the measured current flow rate.
When calibrating the flow rate controller which controls the flow rate of a first gas out of the above-mentioned two or more kinds of gases, particles (for example, molecules) constituting the first gas adhere onto a wall surface defining a chamber and the surface of a stage inside the chamber. When the etching using the above-mentioned two or more kinds of gases is sequentially performed on a plurality of workpieces in a state in which the particles constituting the first gas adhere to the wall surface and the stage, a difference may occur between the result of etching of a film of the workpiece initially processed and the result of etching of a film of the workpiece finally processed. Therefore, there is a need to reduce a difference in etching result between films of workpieces processed sequentially after calibration of a flow rate controller.